duction, but proceeds from some previously existing life or parent. Hence, he has held, and has aimed to show, that fermentation can never take place if all access of germs to a fermentable substance is prevented. From fermentation he has extended his theory of the agency of microscopic organisms in working changes, to the explanation of the origin and multiplication of various infectious diseases, each of which, as well as each kind of fermentation and putrefaction, is caused by its own specific organism.
M. Pasteur took a prominent and most active part in the controversy respecting spontaneous generation, which raged quite bitterly a few years ago. He performed the most decisive experiments that were made, and has contributed more than any other person to turn the current of scientific thought against that theory, and to bring the weight of opinion in favor of his own theory of panspermy. The controversy on this subject, which had been resting for many years after the researches of Siebold, Leuckart, and others, into the mode of development of sexless parasites, was reopened as to the infusoria in 1858 by Pouchet, who affirmed that previous experiments in regard to boiled infusions were inexact, and that boiling did not prevent the appearance of infusorial life, as it would necessarily do if such appearance was dependent on the existence of living organisms or germs in the liquids previous to boiling. M. Pasteur, having become interested in this subject through his studies in fermentation, came forward with his test experiments. The question seemed a very difficult one, and incapable of a definite solution, so that Pasteur's friends, Biot and Dumas, were impelled to counsel him against wasting too much time upon it. They had, however, good reason afterward to revise their opinions. M. Pasteur boiled a suitable organic infusion in glass flasks, which he sealed hermetically while the boiling was going on, so as to exclude the air that might bring in new germs to take the place of those which the boiling had killed. The flasks were then taken to different localities, where, after a time, the necks were broken and air was admitted to the boiled infusion. Pasteur reasoned that if the organisms, which were produced in the liquid on exposure to the atmosphere, were spontaneous growths excited to life by the action of the atmosphere alone, the products would be the same wherever the bottles were broken; but if the manifestation of life depended upon the introduction of new organisms or their germs from the air—since the air of different places would probably contain different organisms and be charged in different proportions with them—there would be different results in different places. The experiments showed manifest differences, in accordance with Pasteur's anticipations, and were considered to demonstrate the existence in the atmosphere of extraneous particles, the introduction of which into an infusion was the necessary condition of life appearing there. Professor Tyndall says of them that they, "carried out with a severity perfectly obvious to the instructed scientific
